Method and device for generating energy during the rolling of a type fitted on a rim

ABSTRACT

A device for generating energy in a rolling wheel includes at least one part that can move with respect to a wheel rim. The at least one part is engaged with elastic means that keep it in contact with a predetermined bead portion of a tyre. The at least one part undergoes reciprocating outward and return motion against action of the elastic means, as a result of forces induced in the at least one part by contact pressure that varies cyclically during each tyre revolution and is exerted on the at least one part by the predetermined bead portion. Also disclosed is a method for generating energy in a rolling wheel that includes subjecting at least one part of the wheel to elastic force that keeps the at least one part in contact with the predetermined bead portion, and subjecting the at least one part to the cyclically-varying contact pressure.

[0001] The present invention relates to a method and a device forgenerating energy which can be used, for example, for carrying outoperations with pressurized air during the rolling of a tyre fitted on arim, and, in particular, for supplying compressed air which can be usedto obtain the desired pressure level within the tyre during the runningof a motor vehicle.

[0002] During the operation of a motor vehicle, a knowledge of the valueof the tyre pressure is an extremely important factor for the continuouscontrol of the tyres and for ensuring safe travel of the motor vehicle.This is because keeping the pressure at the specified value enables thebest possible performance to be obtained from the tyre in terms of wear,rolling resistance, roadholding, braking etc., and affects the safety ofthe driving of the motor vehicle.

[0003] There are known devices designed to generate pressurized air tobe sent into a tyre of a motor vehicle during running.

[0004] U.S. Pat. No. 5,409,049 describes an apparatus for pressurizing atyre fitted on a wheel. The apparatus includes a displacement-type airpump consisting of a free and oscillating piston body provided with areciprocating linear motion by the action of forces produced by therotary motion of the wheel. The apparatus also includes support meansfor supporting the piston without friction during its oscillation withinthe pump, in order to generate pressurized air. It also includessuitable mounting means for fixing the pump to the wheel on which a tyreis fitted in such a way that the path of reciprocating motion of thepiston is out of alignment with the centre and forms a tangent to a pathof rotation of the wheel. Additionally, it includes suitable connectionmeans for introducing into the tyre the pressurized air generated by thepump.

[0005] U.S. Pat. No. 5,667,606 describes an apparatus for pressurizing atyre fitted on a wheel. The apparatus includes a displacement-type airpump, consisting of a combination of a cylinder and a spring-loadedpiston. The pump has a casing suitable for being fixed axially to thewheel. The apparatus also includes a connecting conduit for pressurizedair, suitable for introducing into the tyre the pressurized airgenerated by the pump. The apparatus also includes a cam and a camfollower mounted in the casing. The cam follower engages with the cam tocreate relative movements between them, caused by the cam, and isconnected to the pump in order to drive it. A pendulum is mounted in thecasing so that it rotates freely with respect to it. The pendulum isconnected to one of the said cam and cam follower to keep this componentessentially stationary with respect to the other, while the other ofthese components is fixed to the casing so that it rotates with it andprovides the movement which drives the pump. The cylinder and pistoncombination has an axis of reciprocating motion of the piston in thecylinder which is essentially aligned with the axis of rotation of thewheel.

[0006] The apparatus of U.S. Pat. No. 5,409,049 makes use of the energypotentially contained and/or generated by a wheel of a motor vehiclewhen it is rotating. In particular, the apparatus makes use of thevariation of the gravitational energy (weight) which occurs when use ismade of a body which has an intrinsic weight applied to the wheel andwhich is free to move with respect to the rotating wheel.

[0007] The apparatus of U.S. Pat. No. 5,667,606 uses a cam, a camfollower and a pendulum to convert the rotary motion of the wheel intoreciprocating motion of the pump piston.

[0008] These known apparatus are complicated, delicate and expensive.Moreover, they are positioned on the outside of the wheel. They aretherefore subject to stresses and deformations which can cause frequentfailure.

[0009] Another disadvantage lies in the fact that the application to thewheel of a body (a free oscillating piston or pendulum) having aspecific intrinsic weight necessitates a precise balancing of not onlythe tyre but also the wheel, in order to achieve an acceptableuniformity of operation.

[0010] The objects of the present invention are a device and method forgenerating energy which can be used, for example, in order to carry outoperations with pressurized air suitable for pressurizing a tyre duringthe running of a motor vehicle, which avoids the disadvantages of theknown apparatuses.

[0011] In a first aspect, the invention relates to a device forgenerating energy in a rolling wheel, the said wheel including a tyrefitted on a rim, the said tyre having beads in contact with the saidrim, characterized in that it includes at least one part which can movewith respect to the said rim, the said moving part engaging with elasticmeans which keep it in contact with a predetermined portion of one ofthe said beads, the said moving part being provided with a reciprocatingoutward and return motion, against the action of the said elastic means,as a result of forces induced in the said moving part by a contactpressure which varies cyclically during each revolution of the said tyreand is exerted on the said moving part by the said predetermined portionof bead.

[0012] In a second aspect, the invention relates to a method forgenerating energy in a rolling wheel, the said wheel including a tyrefitted on a rim, the said tyre having beads in contact with the saidrim, characterized in that it includes the steps of

[0013] subjecting at least one part moving with respect to the said rimto an elastic force which keeps it in contact with a predeterminedportion of one of the said beads,

[0014] subjecting the said moving part, by means of the predeterminedportion of bead, to a contact pressure which varies cyclically duringeach revolution of the said tyre to induce in the said moving partforces capable of making it move with a reciprocating motion against theaction of the said elastic force.

[0015] The energy generated by means of the said method and device is ofthe mechanical type. The present invention proposes the use of thisenergy in its initial state or its conversion to any other type ofenergy, such as electrical energy.

[0016] In a third aspect, the invention relates to a device forgenerating energy which can be used to carry out operations withpressurized air during the rolling of a tyre fitted on a rim, the saidtyre having beads in contact with the said rim, the said deviceincluding at least one plunger element and a chamber in which the saidplunger element is capable of moving with a reciprocating motion, thesaid chamber being provided with first and second valve means, the saidfirst valve means being capable of putting the said chamber intocommunication with the external environment, characterized in that thesaid at least one plunger element includes a part which can move withrespect to the said rim, the said moving part engaging with elasticmeans which keep it in contact with a predetermined portion of one ofthe said beads, the said predetermined portion of bead exerting on thesaid moving part a contact pressure which varies cyclically during eachrevolution of the said tyre, the said cyclic variation of contactpressure inducing in the said moving part forces capable of making itmove against the action of the said elastic means and of causing thesaid plunger element to carry out alternate outward and return strokesin the said chamber to compress air present in the said chamber and tomake it flow through the said second valve means and to draw air fromthe external environment through the said first valve means.

[0017] In one embodiment, the said plunger element consists of the saidmoving part and the said elastic means consist of at least one springwhich supports the said moving part in the said chamber, keeping it in apredetermined position with respect to the said rim and in contact withthe said portion of bead.

[0018] In another embodiment, the said plunger element consists of thesaid moving part and a plate, these components being integral with eachother and inclined at a predetermined angle to each other, and the saidelastic means consist of a torsion spring pivot which rotatably supportsthe said plunger element and allows the said plate to rotate in the saidchamber and allows the said moving part to rotate in a cavity of thesaid rim, the said moving part being held by the said torsion springpivot in a predetermined position with respect to the said rim and incontact with the said portion of bead.

[0019] In a further embodiment, the said plunger element consists of thesaid moving part and a piston, these components being integral with eachother, the longitudinal axis of the said moving part and of the saidpiston lying in an essentially radial direction with respect to the saidrim, the said piston being movable in the said chamber, and the saidelastic means consisting of at least one spring which supports the saidmoving part in a cavity of the said rim, holding it in a predeterminedposition with respect to the said rim and in contact with the saidportion of bead.

[0020] The position of the start of the plunger stroke with respect tothe rim is determined by the equilibrium between the pre-loading of thespring and the opposing force due to the total rigidity of the beadmixture and of a metallic bead wire which is included in the bead in aconventional way. This start of stroke position can be flush with therim, or above or below it, and is determined according to the desiredstroke of the plunger element.

[0021] Preferably, the said moving part and the said piston are joinedby a rod provided with an adjustable stroke limiting means.

[0022] Advantageously, the said moving part is a disc housed in a seatin the said rim.

[0023] Typically, the said second valve means are capable of putting thesaid chamber into communication with the interior of the said tyre.

[0024] Preferably, the said device also includes a compressed airreservoir communicating with the said chamber through the said secondvalve means.

[0025] Even more preferably, the said reservoir communicates with theinterior of the said tyre through further valve means capable of makingthe said compressed air flow into the interior of the said tyre.

[0026] Advantageously, the said device is operationally connected to aregulating unit, which includes a pressure sensor capable of measuringthe pressure within the said tyre, and a control unit capable of causingthe opening and closing of the said further valve means to regulate theinflation pressure of the said tyre according to a predeterminedmapping.

[0027] The device according to the invention is based on a phenomenonwhich has been observed by the applicant during the rolling of a tyrefitted on a rim. This phenomenon consists in a cyclic variation of thecontact pressure which is found between the surface of the tyre bead andthe corresponding surface of the rim. This cyclic variation of contactpressure is used in the present invention to generate energy which canbe used for moving mechanical members. In the specific embodiment of theinvention described below, the said mechanical members are designed togenerate pressurized air which can be used to regulate the inflationpressure of the rolling tyre.

[0028] Essentially, in the device according to the invention, the movingpart slides or rotates in the chamber or in the cavity of the rim and iskept in contact with the rim by the elastic means. The variation ofcontact pressure between the bead and the rim which occurs during therolling of the tyre causes the moving part to be displaced in thechamber or in the cavity of the rim against the action of the elasticmeans. As it is displaced, the moving part causes a change of volume inthe chamber and consequently generates a flow of pressurized air. Thepressurized air is sent into a reservoir in which it is stored. When thepressure inside the tyre is lower than the predetermined level, thepressurized air passes from the reservoir to the interior of the tyre.When the pressure inside the tyre reaches the predetermined level andthe reservoir is full, the excess air is discharged to the exterior. Thefirst and second valve means ensure the correct flow of air into and outof the chamber.

[0029] The device according to the present invention uses the variationof contact pressure which occurs, during the rolling of the tyre, in apredetermined contact area between the bead and the rim, and requiresonly minor modifications of the rim, while it does not require bodies ormechanisms associated with the moving tyre or with an external energysource.

[0030] The device according to the invention enables the pressure insidethe tyre to be brought to the requisite levels at each instant. Thus thewear and rolling resistance are minimized, and optimal roadholding andefficient braking are provided. The device according to the inventiontherefore makes the driving of the motor vehicle safer.

[0031] More particularly the device makes it possible to modify thelevel of pressure inside the tyre in relation to the running conditionsof the vehicle. For example, it is possible to have a lower pressureinside the tyre during running in urban areas, where rough and irregularroad surfaces are frequently encountered, and a higher pressure duringrunning outside urban areas, generally on roads with very smoothsurfaces, where the vehicle can travel at higher speed. Thus comfort isoptimized during running in urban areas and fuel consumption isoptimized during running outside urban areas. In other situations also,during the movement of the vehicle, it is possible to have lower tyrepressures, for example when greater traction is required (for running onsnow), or higher pressures, for example in high speed travel with heavyloads and/or in climatic conditions with very high temperatures.

[0032] The active regulation of pressure inside the tyres during therunning of the motor vehicle can be combined with the active regulationof the rigidity and the damping of the suspension with the aim of amarked improvement of the comfort and roadholding. This permits optimalcontrol of the motor vehicle in terms of safety, comfort and fuelconsumption, since all interventions are controlled in an integratedway.

[0033] In a fourth aspect, the present invention relates to a rim for atyre, provided with a device for generating energy which can be used tocarry out operations with pressurized air during the rolling of the saidtyre, the said device including at least one plunger element and achamber in which the said plunger element can move with a reciprocatingmotion, the said chamber being provided with first and second valvemeans, the said first valve means being capable of putting the saidchamber into communication with the external environment, characterizedin that the said at least one plunger element includes a part which canmove with respect to the said rim, the said moving part engaging withelastic means which hold it in a predetermined position with respect tothe said rim so that it comes into contact with a predetermined portionof a bead of the said tyre, the said predetermined portion of beadexerting on the said moving part a contact pressure which variescyclically during each revolution of the said tyre, the said cyclicvariation of contact pressure producing forces on the said moving partwhich are capable of causing it to move against the action of the saidelastic means and of causing the said plunger element to carry outalternate outward and return strokes in the said chamber to compress airpresent in the said chamber and to force it to flow through the saidsecond valve means, and to draw air from the external environmentthrough the said first valve means.

[0034] In a fifth aspect, the present invention relates to a wheel for amotor vehicle, having a tyre fitted on a rim and a device mounted on thesaid rim for generating energy which can be used to carry out operationswith pressurized air during the rolling of the said tyre, the said tyrehaving beads in contact with the said rim, the said device including atleast one plunger element and a chamber in which the said plungerelement can move with a reciprocating motion, the said chamber beingprovided with first and second valve means, the said first valve meansbeing capable of putting the said chamber into communication with theexternal environment, characterized in that the said at least oneplunger element includes a part which can move with respect to the saidrim, the said moving part engaging with elastic means which hold it in apredetermined position with respect to the said rim so that it comesinto contact with a predetermined portion of one of the said beads, thesaid predetermined portion of bead exerting on the said moving part acontact pressure which varies cyclically during each revolution of thesaid tyre, the said cyclic variation of contact pressure producingforces on the said moving part which are capable of causing it to moveagainst the action of the said elastic means and of causing the saidplunger element to carry out alternate outward and return strokes in thesaid chamber to compress air present in the said chamber and to force itto flow through the said second valve means, and to draw air from theexternal environment through the said first valve means.

[0035] Characteristics and advantages of the invention will now beillustrated with reference to embodiments shown by way of example,without restrictive intent, in the attached figures in which:

[0036]FIG. 1 is a partial view, in cross section, of a tyre and a rimwith which is associated a device for generating mechanical energy, madeaccording to the invention;

[0037]FIG. 2 is a sectional view along the plane II-II of FIG. 1;

[0038]FIG. 3 is a partial view, in cross section, of a tyre and a rimwith which is associated a device for generating mechanical energy whichis a variant of that in FIG. 1;

[0039]FIG. 4 is a sectional view along the plane IV-IV of FIG. 3;

[0040]FIG. 5 is a side view of a tyre which is rolling on the ground;

[0041]FIG. 6 is a graph showing the variation of the pressures along acontact line in a transverse direction between a bead of a tyre and arim, in two diametrically opposite positions of the tyre;

[0042]FIG. 7 is a graph showing the cyclic variation of the pressures ona contact area between the bead and rim along three differentcircumferential lines;

[0043]FIGS. 8, 9 and 10 show another variant of the device forgenerating mechanical energy shown in FIG. 1;

[0044]FIG. 11 is a graph which shows a characteristic of a spring of thedevice of FIG. 8;

[0045]FIG. 12 shows a variant of the device of FIG. 8;

[0046]FIG. 13 is a graph which shows the variation, during a wheelrevolution expressed in degrees, of forces per unit of circumferentiallength, acting in the device of FIG. 12 for different values ofinflation pressure;

[0047]FIG. 14 shows schematically a rim provided with four devices forgenerating mechanical energy;

[0048]FIG. 15 shows schematically a unit for active regulation of thepressure inside the tyre of FIG. 1 or FIG. 3;

[0049]FIG. 16 shows schematically an apparatus for regulating thepressure inside the tyre of FIG. 1 or FIG. 3.

[0050]FIGS. 1 and 2 show part of a wheel 1 for a motor vehicle,including a tyre 2 and a rim 3 on which the tyre is fitted. The tyre hasa bead 4 which is housed in a seat 5 of the rim 3. The seat 5 is formedby a base 6 and a rim wall 7. The wheel 1 is associated with a device 10for generating energy, particularly mechanical energy, which in theillustrated case is used to carry out operations with pressurized airduring the rolling of the tyre 2. The device 10 includes a plungerelement 11 and a chamber 12 lying under this element, in which theplunger element 11 can slide with a reciprocating motion in an airtightway. The plunger element 11 is formed by a moving part consisting of adisc 9, separate from the base 6 of the rim and housed in a cylindricalseat 8. The chamber 12 is formed in a structure 13 which is fixed to therim 3 by screws 14. The disc 9 is supported in the chamber 12 byBelleville springs 15 which keep it in contact with a surface portion 16of the bead 4 and flush with the base 6 of the rim 3. Similar resultsare obtained if laminated springs, leaf springs, coil springs or thelike are used in place of Belleville springs.

[0051] The portion of bead 16 exerts a contact pressure on the plungerelement 11, this pressure varying cyclically during each revolution ofthe wheel 1, and induces in this element forces which can make it moveagainst the action of the springs 15, as illustrated below withreference to FIG. 7.

[0052] The chamber 12 is provided with two non-return valves 17 and 18(FIG. 2) including, respectively, a truncated conical shutter 19,subject to the action of a spring 20, and a truncated conical shutter21, subject to the action of a spring 22.

[0053] The valves 17 and 18 put the chamber 12 into communication with acompartment 23 and a compartment 24 respectively, formed in thestructure 13. The compartment 23 communicates freely with the externalenvironment through an aperture 25. The compartment 24 communicates,through an aperture 26, with a pressurized air storage reservoir 27which is fixed to the structure 13 by screws 28. The reservoir 27, inturn, is connected to an ordinary tyre pressurization valve or to asolenoid-operated valve which performs a similar function.

[0054] In another embodiment of the invention, the reservoir 27 isconnected to a compressed-air turbine which supplies the operatingenergy to other devices or services located on the wheel.

[0055] The device 10 operates by making use of the variation of thecontact pressure, observed by the applicant, which occurs, during therolling of the tyre 2, between the surface portion 16 of the bead 4 andthe rim 3 on which the tyre 2 is fitted.

[0056] During the rolling of the tyre, the contact area between the bead4 and the rim 3 is initially close to the road surface, immediatelyabove the footprint, and is subsequently distant from the footprint. InFIG. 5, the portion of the tyre located in the footprint is delimited byA and B. As it moves from the position AB of FIG. 5 to the oppositeposition D (known in the art as the “over-inflated area”), the profileof the tyre sidewalls is modified and the reactive forces between thebeads and the rim vary.

[0057] The applicant has observed that the contact pressures between thebead and the rim vary according to the position along the axialdevelopment of the contact line between the bead and the rim. Thiscontact line is formed by the intersection of the bead with a transversesection plane, as shown in the insert in the graph of FIG. 6. The graphof FIG. 6 shows the variation of the bead-rim contact pressures inflattening with a load of 600 kg. It can be seen that, in conditions ofsimple inflation, the distribution of contact pressures at the rim isidentical at all circumferential positions. In vertical load conditions(flattening), the distribution of pressures at the rim changes with thecircumferential position, and the variation of the contact pressuresbetween the bead and the rim is represented by the curve e in FIG. 6 inthe centre of the footprint (point C in FIG. 5) and is represented bythe curve d at the opposite point (point D in FIG. 5).

[0058]FIG. 7 shows the (cyclical) variations of the contact pressuresbetween the bead and the rim under load from the circumferentialposition (in other words along the circumferential development of thebead), at the nodes (points) a, b, c, shown in the drawing of the beadplaced at the side. The variation of the rim pressure at the node a isrepresented by the curve l while the variation at the node b isrepresented by the curve m and the variation at the node c isrepresented by the curve n. The curve l shows that the pressure betweenthe bead and the wall of the rim in contact with the bead undergoes avariation, during one cycle of rotation of the tyre, consisting in anessentially sinusoidal oscillation moving from a normal constant valueto a minimum value L when the node a is in the centre of the footprint(the 180° position). The curve m shows that the pressure undergoes avariation consisting in an essentially sinusoidal oscillation movingfrom a normal constant value to a maximum value M when the node b is inthe centre of the footprint. The curve n shows that the pressure at thenode c remains essentially constant during the whole cycle of rotationof the tyre.

[0059] The curves l, m and n of FIG. 7 relate to the nodes, or points,a, b and c of the bead, and therefore relate to what takes place indifferent positions of the bead-rim contact surface during one cycle ofrotation of the tyre. By an analysis of these curves, carried out forexample by the finite elements calculation method, it is possible toselect the optimal position (in other words, the position with thegreatest variation of contact pressure) in which the device to which theinvention relates can be located.

[0060] The device 10 according to the invention makes use of thevariation of the contact pressure which takes place in one cycle ofrotation of the tyre, in the area of the node b, defined as the optimalnode, for generating energy. In the type of application described here,this energy is used to generate compressed air which can be used toregulate the pressure of the tyre during the running of the motorvehicle.

[0061] When a given tread area of the tyre comes into the proximity ofthe contact with the ground (point A in FIG. 5), the contact pressure inthe corresponding surface portion 16 of the bead which is in contactwith the disc 9 of the plunger element 11 increases from the normalconstant value to the maximum value M (curve m in FIG. 7). In theseconditions, the surface portion 16 of the bead exerts on the plungerelement 11 a force capable of overcoming the pre-loading of theBelleville springs 15 and making the element slide in an airtight way inthe chamber 12, from the start of the stroke position in FIG. 1 to thestroke end position in FIG. 2. The plunger element 11 thus carries outan outward stroke in which it compresses the air present inside thechamber 12 until it reaches the value capable of opening the valve 18,overcoming the force exerted by the spring 23 on the shutter 22. Thepressurized air flows through the valve 18 from the chamber 12 towardsthe compartment 24 and the reservoir 27. From the reservoir 27 it issent to the ordinary pressurization valve of the tyre 2, or to asolenoid-operated valve which carries out similar functions when the airpressure inside the tyre has to be regulated.

[0062] When the aforesaid tread area moves away from the centre of thefootprint and then leaves it (point B in FIG. 5), the pressure in thesurface portion 16 of the bead, at the interface with the plungerelement 11, decreases from the maximum value M to the normal constantvalue (curve m in FIG. 7). The plunger element 11 is pushed by theBelleville springs 15 so that it slides into the chamber 12 until it isagain flush with the base 6 of the rim 3. In the return stroke, theplunger element 11 creates within the chamber 12 a pressure drop whichcauses the valve 17 to open by overcoming the force exerted by thespring 20 on the shutter 19. Thus the external air flows from thecompartment 23 through the valve 17 into the chamber 12, where it iscompressed by the plunger element 11 during the next revolution of thewheel 1.

[0063]FIGS. 3 and 4 show a device 110 for generating mechanical energy,which in this case also is used to carry out operations with pressurizedair, associated with the tyre 2 and the rim 3. The device 110 includes aplunger element 111 which, in turn, includes a moving disc 30 and aplate 31. The disc 30 and the plate 31 are integral with each other andinclined at a predetermined angle to each other. The plunger element 111therefore has the shape of a lever with two arms. The disc 30 is housedin a seat 37 of the base 6. The plunger element 111 is rotatablysupported in a structure 32 by a pivot 33 formed by a torsion spring.The structure 32 is fixed to the rim 3 by screws 34, and a structure 35is fixed to the rim 3 and to the structure 32 by screws 36. A cavity 101in which the disc 30 can rotate is formed in the structure 32. A chamber112 in which the plate 31 can rotate is formed in the structure 35. Thechamber 112 is provided with the non-return valves 17 and 18 which putit into communication with the compartments 23 and 24 respectively. Thecompartments 23 and 24, in turn, communicate, respectively, with theexternal environment and with the pressurized air storage reservoir 27.

[0064] The torsion spring pivot 33 keeps the plunger element 111 at thestart of the stroke, as shown in FIG. 3, in which the disc 30 is flushwith the base 6 of the rim 3 and is in contact with the surface portion16 of the bead 4. The surface portion 16 of the bead exerts on theplunger element 111 a contact pressure which varies cyclically with thevariation represented by the curve m in FIG. 7.

[0065] The device 110 operates in a similar way to the device 10 ofFIGS. 1 and 2.

[0066] When the pressure at the interface between the surface portion 16of the bead and the disc 30 increases from the normal constant value tothe maximum value M (curve m in FIG. 7), the surface portion 16 of thebead exerts on the disc 30 a force capable of overcoming the action ofthe torsion spring of the pivot 33, and of making the plunger element111 rotate in the clockwise direction according to FIG. 3. The plungerelement 111 moves from the start of the stroke, represented in solidlines, to the end of the stroke, represented by a broken line in FIG. 3.The disc 30 rotates in the cavity 101 and the plate 31 rotates in thechamber 112. The plate 31 carries out an outward stroke in which itcompresses the air present inside the chamber 112 until the air pressurereaches a level capable of opening the valve 18. The pressurized airtherefore flows from the chamber 112 towards the compartment 24 and thereservoir 27.

[0067] When the pressure at the interface between the surface portion 16of the bead and the disc 30 decreases from the maximum value M to thenormal constant value (curve m in FIG. 7), the plunger element 111 ispushed by the torsion spring of the pivot 33 so that it rotates in theanti-clockwise direction according to FIG. 3. The disc 30 and the plate31 carry out a return stroke, creating a pressure drop inside thechamber 112, until the disc 30 is again flush with the base 6 of thebead 4. When the pressure drop reaches the value capable of opening thevalve 17, the external air flows from the compartment 23 into thechamber 112, where it is compressed in the next revolution of the wheel1.

[0068] The plunger element 111 is shaped in the form of a lever with ashorter arm 30 and a longer arm 31. This enables the compression ratioto be increased above that of the device 10, and makes it possible toutilize the cyclic variation of the arm of the resultant of thedistribution of the contact pressure.

[0069] The position of the start of the stroke of the plunger element 11or 111 with respect to the base 6 of the rim is determined by theequilibrium between the pre-loading of the spring 15 or 33 and theopposing force due to the rigidity of the mixture of the bead 4 and of abead wire (not shown) which is conventionally included in the bead.

[0070] The rigidity of the mixture of the bead and of the rim variesfrom 10 to 18 MPa.

[0071] In the embodiments shown in FIGS. 1, 2, 3 and 4, the plungerelements 11 and 111 have a start of stroke position in which the discs 9and 30 are flush with the base 6. However, the discs could be in aposition above or below the base 6. The start of stroke position isselected according to the stroke of the plunger element. The length ofthe stroke depends on the deformability of the bead, and, in particular,on the rubber compressed between the radially inner surface of the beadwire and the surface of the rim, the elastic means chosen, and the typeof tyre used. The length of this stroke lies in the range from 1.5 to 5mm and is, for example, 2-2.5 mm.

[0072] It should be noted that these excursion values are not large inabsolute terms, but the frequency of the excursion is considerable. At aspeed of 120 km/hr, for example, it is of the order of 20 cycles persecond, varying with the size of the tyre.

[0073]FIG. 8 shows a device 210 for generating mechanical energy whichcan be used to carry out operations with pressurized air during therolling of the tyre 2. The device 210 includes a plunger element 211which, in turn, includes a moving disc 203, a rod 205 and a piston 214.The rod 205 is integral with the disc 203 and with the piston 214. Thedisc 203 is housed in a cavity 201 of the base 6; the springs 202 keepit in contact with the surface portion 16 of the bead. The disc 203slides in the cavity 201, and springs 202 cause the disc 203 to lie in astart of stroke position in which it is raised with respect to the base6 in such a way that its stroke is facilitated. The cavity 201 isprovided with a hole 206 (FIG. 10) into which the rod 205 passes. A seal207, surrounding the rod 205 and ensuring the airtightness of the cavity201, is fitted in the hole 206. The rod 205 is integral with a strokelimiter 204. The rod 205 extends into a recess 215 formed in a spoke 213of the rim 3. In the spoke 213 there is also a chamber 212 in which thepiston 214 can slide in an airtight way. The longitudinal axis of thedisc 203, the rod 205 and the piston 214 lies along a radius R of thespoke 213. The chamber 212 is provided with non-return valves 17 and 18which put it into communication, respectively, with the externalenvironment and with the pressurized air storage reservoir 27.

[0074] With each revolution of the wheel 1, the disc 203 is subjected tothe action of forces which vary as a result of the cyclic oscillation ofthe contact pressure which the surface portion 16 of the bead exerts onthe disc 203. In the presence of these forces, the disc 203 moves with areciprocating motion in the cavity 201, being displaced in the radialdirection along the directrix R from the position shown in FIG. 8 to theposition shown in FIG. 9, and vice versa.

[0075] The reciprocating motion of the disc 203 is transmitted to thepiston 214 through the rod 205. The piston 214 slides in an airtight wayin the chamber 212 and carries out alternate outward and return strokes,moving in the radial direction along the directrix R. In the outwardstrokes, the piston 214 compresses the air present within the chamber212 and discharges it through the valve 18, and in the return strokes itdraws air from the exterior through the valve 17.

[0076] The plunger element 211 can be miniaturized to limit the overalldimensions and weight.

[0077] In order to apply the device 210 to a 205/55 R16 tyre, a spring202, having the mechanical load (force)-compression characteristic shownin FIG. 11, was selected. FIG. 11 shows that, after a first part of thecurve with a very steep slope (high rigidity), there is a practicallyflat part (low rigidity). The point of change of slope is reached at aload of 700 N and a compression of 10 mm. The springs 202 are calibratedin such a way that they operate with a specified travel of 2.5 mm inresponse to a force variation of a few tens of newtons (the areaidentified by a rectangle in FIG. 11). The springs 202 therefore operatein the less sloping part of the curve, having “absorbed” a staticpre-loading (due to the contact pressure between the surface portion 16of the bead and the disc 203, in the position shown in FIG. 8) as shownby the steeply sloping part of the characteristic curve.

[0078] In other embodiments of the invention, the rod 205 can beconnected to suitable mechanisms, of the crankshaft and connecting rodtype or the rack and pinion type for example, which are known and aretherefore not shown here, to operate devices capable of generating otherkinds of energy, for example electrical energy for supplying sensors andtransducers of various types which may be fitted on the wheel.

[0079]FIG. 12 shows a device 310 for generating mechanical energy whichcan be used for carrying out operations with pressurized air, which is avariant of the device of FIG. 8 and in which identical parts areindicated by the same numbers.

[0080] The rod 205, which links the disc 203 and the piston 214 of theplunger element 211, is provided with a nut 331 which acts as a strokelimiter. By adjusting the nut 331, it is possible to modify the freetravel of the springs 202 and consequently the minimum load Fmin to beapplied to the plunger element 211 in order to obtain even a minimumexcursion of the piston 214. In the device 310, the end of strokeposition 331 is selected according to the pressure which is to bemaintained within the tyre during its rolling.

[0081] The device 310 is based on a phenomenon, observed by theapplicant, by which, as the internal pressure of the tyre varies, theforce F per unit of circumferential length due to the contact pressurein the portion of surface 16 between the bead and rim varies as shown bythe curves p, r and s in FIG. 13, as a function of the circumferentialposition expressed in degrees. The curves p, r and s relate to differentvalues of inflation pressure (1.8 bars, 2.2 bars and 2.5 barsrespectively) and show that the mean value of the force F varies withthe inflation pressure of the tyre and increases as the inflationpressure decreases. In turn, the excursion of the force, in other wordsthe difference between the maximum and minimum value of the force,during one revolution of the wheel, increases significantly as thepressure decreases, as shown in FIG. 13.

[0082] The device 310 makes it possible to restore and maintain apredetermined pressure within the tyre even when the inflation pressuretends to decrease. Since the mean value of the contact force F betweenthe bead and the disc 203 decreases as the internal pressure of the tyreincreases, the force F acting on the plunger element 211 becomes lessthan the minimum value Fmin when a predetermined pressure is reached.When the value of the contact force F falls below the valuecorresponding to the desired internal pressure, the stroke limiter 331prevents the plunger element 211 from moving to a larger radius andtherefore prevents its excursion. The plunger element 211 is blocked andthe device 310 ceases to generate pressurized air. The blocking pointdepends on the calibration of the springs 202 and on the position of thestroke limiter 331.

[0083] The principal advantage of the device 310 consists in the factthat the efficiency of pumping increases as the internal pressure of thetyre decreases, since the differences between the maximum and minimumforce F increase during the cycle as the inflation pressure decreases.This provides efficient, rapid and safe reinflation of the tyre whennecessary, in other words when the internal pressure is low. When thenominal operating pressure, for example 2.5 bars, is reached, thepumping efficiency is reduced, ensuring that the optimal pressure is notexceeded.

[0084] Thus the operating cycles of the plunger element are reduced andthe generation of compressed air is prevented when it is not required,and therefore compressed air does not have to be vented to the exteriorof the tyre.

[0085] The described devices 10, 110, 210 and 310 can be fitted in aplurality of positions, for example 4 or 6 positions, which are spacedat equal intervals along the circumference of the rim under the bead(FIG. 14). Each device stores air in a corresponding reservoir 27 andthe different reservoirs which may or may not communicate with eachother (in the centre if they extend radially, or laterally if theyextend circumferentially).

[0086] The described devices 10, 110, 210 and 310 can be used for activeregulation of the pressure within the tyre 2.

[0087]FIG. 15 is a block diagram of a unit 40 for active regulation ofthe pressure within the tyre 2. The unit 40 includes a sensor 41 formeasuring the pressure within the tyre, a device 10 or 110 or 210 or 310for generating mechanical energy which can be used to carry outoperations with pressurized air, a controller 42 capable of controllingthe inflation pressure of the tyre according to mappings defined bysuitable algorithms, and a solenoid-operated tour-way valve 43 whichputs the reservoir 27 into communication with the interior of the tyre 2and puts the interior of the tyre 2 into communication with the externalenvironment. The controller 42 makes the solenoid-operated valve 43 opento introduce pressurized air into the interior of the tyre, or to removeair from the interior of the tyre, according to the pressure measured inthe tyre, the running conditions and the decisions made by the driver.

[0088]FIG. 16 shows an apparatus 300 for regulating the pressure withinthe tyre, comprising a three-way valve 190, valves 191 and 192, and areservoir 199. The valve 190 is connected through a duct, represented bythe arrow 193, to a device 10 or 110 or 210 or 310 for generatingmechanical energy which can be used to carry out operations withpressurized air, and through ducts 194 and 195 to the valve 191 and thevalve 192 respectively. The valves 191 and 192 are connected throughducts 196, 197 and 198 to the reservoir 199. The reservoir 199, in turn,is connected to the interior of the tyre 2. The valve 190 is operated bya signal generated on board the vehicle, for example a signal emitted bya controller, similar to the controller 42 in FIG. 15, which operates inaccordance with logics for optimizing the behaviour of the motorvehicle, or a signal generated manually by a driver. The valve 190enables the pressurized air from the reservoir 27 of the device 10 or110 or 210 or 310 to flow through the duct 194 or through the duct 195.

[0089] If the pressurized air passes through the duct 194, the valve 191allows the air to enter the reservoir 199 when the pressure within thereservoir is lower than a calibration value p₂. On the other hand, ifthe pressure within the reservoir is greater than the calibration valuep₂, the valve 191 discharges air to the exterior (arrow U1).

[0090] If the pressurized air passes through the duct 195, the valve 192acts in a similar way to the valve 191, but operates at a calibrationpressure p₁ which is different from the pressure p₂.

[0091] The apparatus 300 allows the pressure within the tyre to be heldconstant at the desired value, p₁ or p₂.

[0092] For a 195/65R15 tyre, for example, the pressure value p₁ equal to2.3 bars is optimal for travel outside urban areas, and for lower fuelconsumption, while the value p₂ equal to 2.1 bars is optimal for travelin urban areas.

[0093] The apparatus also has the advantage of eliminating thetroublesome necessity of restoring the pressure value within the tyre atpetrol stations or at appropriate pumping locations.

1. Device (10; 110; 210; 310) for generating energy in a rolling wheel(1), the said wheel (1) including a tyre (2) fitted on a rim (2), thesaid tyre (2) having beads (4) in contact with the said rim (3),characterized in that it includes at least one part (9; 30; 203) whichcan move with respect to the said rim (3), the said moving part (9; 30;203) engaging with elastic means (15; 33; 202) which keep it in contactwith a predetermined portion (16) of one of the said beads (4), the saidmoving part (9; 30; 203) being provided with a reciprocating outward andreturn motion, against the action of the said elastic means (15; 33;202), as a result of forces induced in the said moving part (9; 30; 203)by a contact pressure which varies cyclically during each revolution ofthe said tyre (2) and is exerted on the said moving part (9; 30; 203) bythe said predetermined portion (16) of the bead.
 2. Method forgenerating energy in a rolling wheel (1), the said wheel (1) including atyre (2) fitted on a rim (3), the said tyre (2) having beads (4) incontact with the said rim (3), characterized in that it includes thesteps of subjecting at least one part (9; 30; 203) moving with respectto the said rim (3) to an elastic force which keeps it in contact with apredetermined portion (16) of one of the said beads (4), subjecting thesaid moving part (9; 30; 203), by means of the predetermined portion(16) of the bead, to a contact pressure which varies cyclically duringeach revolution of the said tyre (2) to induce in the said moving part(9; 30; 203) forces capable of making it move with a reciprocatingmotion against the action of the said elastic force.
 3. Device (10; 110;210; 310) for generating energy which can be used to carry outoperations with pressurized air during the rolling of a tyre (2) fittedon a rim (3), the said tyre (2) having beads (4) in contact with thesaid rim (3), the said device (10; 110; 210; 310) including at least oneplunger element (11; 111; 211) and a chamber (12; 112; 212) in which thesaid plunger element (11; 111; 211) is capable of moving with areciprocating motion, the said chamber (12; 112; 212) being providedwith first and second valve means (17, 18), the said first valve means(17) being capable of putting the said chamber (12; 112; 212) intocommunication with the external environment, characterized in that thesaid at least one plunger element (11; 111; 211) includes a part (9; 30;203) which can move with respect to the said rim (3), the said movingpart (9; 30; 203) engaging with elastic means (15; 33; 202) which keepit in contact with a predetermined portion (16) of one of the said beads(4), the said predetermined portion of bead (16) exerting on the saidmoving part (9; 30; 203) a contact pressure which varies cyclicallyduring each revolution of the said tyre (2), the said cyclic variationof contact pressure inducing in the said moving part (9; 30; 203) forcescapable of making it move against the action of the said elastic means(15; 33; 202) and of causing the said plunger element (11; 111; 211) tocarry out alternate outward and return strokes in the said chamber (12;112; 212) to compress air present in the said chamber (12; 112; 212) andto make it flow through the said second valve means (18) and to draw airfrom the external environment through the said first valve means (17).4. Device (10) according to claim 3, characterized in that the saidplunger element (11) consists of the said moving part (9) and the saidelastic means (15) consist of at least one spring which supports thesaid moving part (9) in the said chamber (12), keeping it in apredetermined position with respect to the said rim (3) and in contactwith the said portion of bead (16).
 5. Device (110) according to claim3, characterized in that the said plunger element (111) consists of thesaid moving part (30) and a plate (31), these components being integralwith each other and inclined at a predetermined angle to each other, andthe said elastic means (30) consist of a torsion spring pivot whichrotatably supports the said plunger element (111) and allows the saidplate (31) to rotate in the said chamber (112) and allows the saidmoving part (30) to rotate in a cavity (101) of the said rim, the saidmoving part (30) being held by the said torsion spring pivot (30) in apredetermined position with respect to the said rim (3) and in contactwith the said portion of bead (16).
 6. Device (210) according to claim3, characterized in that the said plunger element (211) consists of thesaid moving part (203) and a piston (214), these components beingintegral with each other, the longitudinal axis of the said moving part(203) and of the said piston (214) lying in an essentially radialdirection with respect to the said rim (3), the said piston (214) beingmovable in the said chamber (212), and the said elastic means (202)consisting of at least one spring which supports the said moving part(203) in a cavity (201) of the said rim, holding it in a predeterminedposition with respect to the said rim (3) and in contact with the saidportion of bead (16).
 7. Device (210) according to claim 6,characterized in that the said moving part (203) and the said piston(214) are joined by a rod (205) provided with an adjustable strokelimiting means (331).
 8. Device (210) according to claim 3,characterized in that the said moving part (9; 30; 203) is a disc housedin a base (6) of the said rim (3).
 9. Device (210) according to claim 3,characterized in that the said second valve means (18) are capable ofputting the said chamber (12; 112; 212) into communication with theinterior of the said tyre (2).
 10. Device (10; 11; 210; 310) accordingto claim 3, characterized in that it also includes a compressed airreservoir (27) communicating with the said chamber (12; 112; 212)through the said second valve means (18).
 11. Device (10; 11; 210; 310)according to claim 10, characterized in that the said reservoir (27)communicates with the interior of the said tyre (2) through furthervalve means (43; 190, 191, 192) capable of making the said compressedair flow into the interior of the said tyre (2).
 12. Device (10; 11;210; 310) according to claim 3, characterized in that it isoperationally connected to a regulating unit (40), which includes apressure sensor (41) capable of measuring the pressure within the saidtyre (2), and a control unit (42) capable of causing the opening andclosing of the said further valve means (43; 190, 191, 192) to regulatethe inflation pressure of the said tyre according to a predeterminedmapping.
 13. Rim (3) for a tyre (2), provided with a device (10; 110;210; 310) for generating energy which can be used to carry outoperations with pressurized air during the rolling of the said tyre (2),the said device (10; 110; 210; 310) including at least one plungerelement (11; 111; 211) and a chamber (12; 112; 212) in which the saidplunger element (11; 111; 211) can move with a reciprocating motion, thesaid chamber (12; 112; 212) being provided with first and second valvemeans (17, 18), the said first valve means (17) being capable of puttingthe said chamber (12; 112; 212) into communication with the externalenvironment, characterized in that the said at least one plunger element(11; 111; 211) includes a part (9; 30; 203) which can move with respectto the said rim (3), the said moving part (9; 30; 203) engaging withelastic means (15; 33; 202), which hold it in a predetermined positionwith respect to the said rim (3) so that it comes into contact with apredetermined portion (16) of a bead (4) of the said tyre (2), the saidpredetermined portion of bead (16) exerting on the said moving part (9;30; 203) a contact pressure which varies cyclically during eachrevolution of the said tyre (2), the said cyclic variation of contactpressure producing forces on the said moving part (9; 30; 203) which arecapable of causing it to move against the action of the said elasticmeans (15; 33; 202) and of causing the said plunger element (11; 111;211) to carry out alternate outward and return strokes in the saidchamber (12; 112; 212) to compress air present in the said chamber (12;112; 212) and make it flow through the said second valve means (18), andto draw air from the external environment through the said first valvemeans (17).
 14. Wheel (1) for a motor vehicle, having a tyre (2) fittedon a rim (3) and a device (10; 110; 210; 310) mounted on the said rim(3) for generating energy which can be used to carry out operations withpressurized air during the rolling of the said tyre (2), the said tyre(2) having beads (4) in contact with the said rim (3), the said device(10; 110; 210; 310) including at least one plunger element (11; 111;211) and a chamber (12; 112; 212) in which the said plunger element (11;111; 211) can move with a reciprocating motion, the said chamber (12;112; 212) being provided with first and second valve means (17, 18), thesaid first valve means (17) being capable of putting the said chamber(12; 112; 212) into communication with the external environment,characterized in that the said at least one plunger element (11; 111;211) includes a part (9; 30; 203) which can move with respect to thesaid rim (3), the said moving part (9; 30; 203) engaging with elasticmeans (15; 33; 202) which keep it contact with a predetermined portion(16) of one of the said beads (4), the said predetermined portion ofbead (16) exerting on the said moving part (9; 30; 203) a contactpressure which varies cyclically during each revolution of the said tyre(2), the said cyclic variation of contact pressure producing forces onthe said moving part (9; 30; 203) which are capable of causing it tomove against the action of the said elastic means (15; 33; 202) and ofcausing the said plunger element (11; 111; 211) to carry out alternateoutward and return strokes in the said chamber (12; 112; 212) tocompress air present in the said chamber (12; 112; 212) and make it flowthrough the said second valve means (18), and to draw air from theexternal environment through the said first valve means (17).